A low-loss microstrip filter

Abstract

The present invention discloses a microstrip filter, microwave circuit, and antenna, comprising an upper microstrip board, a prepreg, and a lower microstrip board. The prepreg is positioned between the upper and lower microstrip boards, and the lower microstrip board is connected to a ground plane. A first microstrip transmission line is provided on the upper layer of the upper microstrip board, and a second microstrip transmission line is provided on the lower layer of the upper microstrip board. The first microstrip transmission line is in a "X" shape, and the second microstrip transmission line is in a "T" shape. The first and second microstrip transmission lines overlap, and the first and second microstrip transmission lines are connected by a metalized blind via. The designed microstrip filter is compact, has low loss, and is easy to integrate.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a microstrip filter, a microwave circuit and an antenna. Background Art

[0002] Filters are widely used in communications, radar, integrated circuits, and other fields. To integrate with antennas, filters must be small, have low loss, and be easy to integrate without compromising antenna performance. In related art, Chinese invention patent application publication number CN107369869A discloses a low-insertion-loss filter based on a packaged microstrip circuit. The filter comprises a bottom dielectric substrate, an intermediate dielectric substrate, an upper dielectric substrate, a metal coating attached to the bottom dielectric substrate, a metal coating attached to the upper dielectric substrate, and an array of metal vias extending through the upper dielectric substrate. Chinese utility model patent publication number CN209747695U discloses a multi-layer, wide-edge coupled broadband filter with notch characteristics. The circuit utilizes a two-layer dielectric and three-layer metal design and consists of three identical resonators. Each resonator consists of a curved T-shaped microstrip patch applied to the upper and lower dielectric surfaces and a circular coupling slot in the middle layer. However, all of the aforementioned filters achieve filtering through a coupled structure, which results in high losses.

[0003] Chinese invention patent application publication number CN115548608A discloses a compact, micro-wideband bandpass filter constructed from three laminated dielectric substrates. However, the bandpass filter designed in this scheme is a planar structure, not a three-dimensional one. Chinese invention patent application publication number CN111710944A discloses a multi-layer, self-encapsulated, ultra-wideband impedance-transforming balun bandpass filter, comprising, from top to bottom, a top metal ground plate, an upper-middle stripline transmission line, a lower-middle stripline transmission line, and a bottom metal ground plate. However, this scheme relies on coupled energy for filtering, resulting in high losses. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to reduce the loss of a microstrip filter.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] A microstrip filter is proposed, comprising: an upper microstrip board, a prepreg, and a lower microstrip board, wherein the prepreg is located between the upper microstrip board and the lower microstrip board, and the lower microstrip board is connected to a ground plate;

[0007] The upper layer of the upper microstrip board is provided with a first microstrip transmission line, and the lower layer of the upper microstrip board is provided with a second microstrip transmission line. The first microstrip transmission line is in a cross shape, and the second microstrip transmission line is in a T shape. The first microstrip transmission line and the second microstrip transmission line overlap, and the first microstrip transmission line and the second microstrip transmission line are connected by a metallized blind hole.

[0008] Furthermore, the ground plate includes a first dielectric substrate and a second dielectric substrate, the first dielectric substrate is located on an upper layer of the lower microstrip board, and the second dielectric substrate is located on a lower layer of the lower microstrip board.

[0009] Furthermore, the first microstrip transmission line and the second microstrip transmission line are copper foils attached to the upper layer and the lower layer of the upper microstrip board, respectively.

[0010] Furthermore, the first microstrip transmission line includes two end lines and a convex line, the convex line is located between the two end lines and forms a coupling region, the second microstrip transmission line includes a first line and a second line, the second line is perpendicular to the first line;

[0011] The first circuit overlaps with the circuits at both ends and is connected via metallized blind vias. The second circuit corresponds to the coupling region and is connected to the convex circuit via metallized blind vias.

[0012] Furthermore, the length of the microstrip filter is 1 wavelength.

[0013] In addition, a microwave circuit is also proposed, comprising the microstrip filter as described above.

[0014] In addition, an antenna is also proposed, comprising the microstrip filter as described above.

[0015] The advantages of the present invention are:

[0016] (1) The present invention sets the shape of the first microstrip transmission line arranged on the top surface of the upper microstrip board to an "X" shape, and sets the shape of the second microstrip transmission line arranged on the bottom surface of the upper microstrip board to a "T" shape, thereby realizing cross-coupling through the "X"-shaped first microstrip transmission line, improving the rectangular coefficient of the filter, reducing the number of filter stages, and realizing miniaturization; the microstrip filter has a simple structure, no interruption in the transmission line, low loss, and capacitive loading is achieved by setting a T-shaped line, so the loss is much smaller than that of the filter with a coupling structure, and the loss is only 1dB.

[0017] (2) The length of a conventional microstrip filter is about 2 to 3 wavelengths under the premise of the same rectangular coefficient, while the length of the microstrip filter designed in the present invention is only 1 wavelength.

[0018] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a schematic structural diagram of a microstrip filter proposed in one embodiment of the present invention;

[0020] Figure 2 1 is a schematic structural diagram of a microstrip line in a microstrip filter according to an embodiment of the present invention;

[0021] Figure 3 1 is a schematic diagram of the connection of microstrip lines in a microstrip filter according to an embodiment of the present invention;

[0022] Figure 4 FIG. 4 is a schematic diagram of simulation results of a microstrip filter proposed in one embodiment of the present invention. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] like Figures 1 to 2 As shown, the first embodiment of the present invention provides a microstrip filter, which includes: an upper microstrip board 10, a prepreg 30 and a lower microstrip board 20, wherein the prepreg 30 is located between the upper microstrip board 10 and the lower microstrip board 20, and the lower microstrip board 20 is connected to a ground plate;

[0025] The upper layer of the upper microstrip board 10 is provided with a first microstrip transmission line 11, and the lower layer of the upper microstrip board 10 is provided with a second microstrip transmission line 12. The first microstrip transmission line 11 is in a cross shape, and the second microstrip transmission line 12 is in a T shape. The first microstrip transmission line 11 and the second microstrip transmission line 12 overlap, and the first microstrip transmission line 11 and the second microstrip transmission line 12 are connected by a metallized blind hole 40.

[0026] In this embodiment, the shape of the first microstrip transmission line 11 provided on the top surface of the upper microstrip board 10 is set to an "X" shape, and the shape of the second microstrip transmission line 12 provided on the bottom surface of the upper microstrip board 10 is set to a T shape. The "X"-shaped first microstrip transmission line 11 is used to achieve cross-coupling, thereby improving the rectangular coefficient of the filter, reducing the number of filter stages, and achieving miniaturization. The T-shaped line is used to achieve capacitive loading, and the loss is much smaller than that of a filter with a coupled structure. The insertion loss of a traditional microstrip filter with the same rectangular coefficient is about 3 to 5 dB, while the loss of the microstrip filter designed in this embodiment is only 1 dB.

[0027] Furthermore, in this embodiment, the microstrip filter is set to a three-layer structure, which can be capacitively loaded in the z direction, the dimensions in the x and y directions can be significantly reduced, and the microstrip filter can be implemented with a minimum number of layers, reducing the difficulty of processing.

[0028] In one embodiment, the ground plane includes a first dielectric substrate 21 and a second dielectric substrate 22 . The first dielectric substrate 21 is located on an upper layer of the lower microstrip board 20 , and the second dielectric substrate 22 is located on a lower layer of the lower microstrip board 20 .

[0029] It should be noted that the closer the first dielectric substrate 21 is to the upper microstrip line, the higher the impedance of the transmission line will be.

[0030] In one embodiment, the first microstrip transmission line 11 and the second microstrip transmission line 12 are copper foils attached to the upper and lower layers of the upper microstrip board 10 , respectively.

[0031] In one embodiment, as shown in FIG. Figures 2 to 3 As shown, the first microstrip transmission line 11 includes two end lines and a convex line, the convex line is located between the two end lines and forms a coupling region, the second microstrip transmission line 12 includes a first line and a second line, the second line is perpendicular to the first line;

[0032] The first circuit overlaps with the circuits at both ends and is connected via metalized blind vias 40 . The second circuit corresponds to the coupling region and is connected to the protruding circuit via metalized blind vias 40 .

[0033] It should be noted that, in this embodiment, the two ends are connected to the first circuit via a metalized blind via 40 respectively, which only connects the first microstrip transmission line 11 and the second microstrip transmission line 12 and cannot penetrate through.

[0034] It should be noted that the convex portion line can be set to a straight line, an arc, a triangle, etc., and this embodiment does not specifically limit it. As long as the first microstrip transmission line 11 is not a straight line and can provide cross coupling.

[0035] In one embodiment, the length of the microstrip filter is 1 wavelength.

[0036] It should be noted that, under the premise of the same rectangular coefficient, the length of a conventional microstrip filter is about 2 to 3 wavelengths, while the length of the microstrip filter designed in this embodiment is only 1 wavelength.

[0037] Figure 4 The simulation results of the microstrip filter in this embodiment are as follows: Figure 4 It can be seen that the out-of-band suppression reaches -30dB and the in-band insertion loss is only -0.17dB, which shows that the filter has high out-of-band suppression and very low in-band loss. The measured results are basically consistent with the simulation results.

[0038] In addition, the present invention also provides a microwave circuit, including the microstrip filter described in the above embodiment.

[0039] In addition, the present invention also provides an antenna, comprising the microstrip filter as described in the above embodiment.

[0040] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0042] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A microstrip filter, characterized in that: The filter comprises: an upper microstrip board, a prepreg and a lower microstrip board, wherein the prepreg is located between the upper microstrip board and the lower microstrip board, and the lower microstrip board is connected to a ground plate; A first microstrip transmission line is provided on the upper layer of the upper microstrip board, and a second microstrip transmission line is provided on the lower layer of the upper microstrip board, wherein the first microstrip transmission line is in an X-shape, and the second microstrip transmission line is in a T-shape, and the first microstrip transmission line and the second microstrip transmission line overlap, and the first microstrip transmission line and the second microstrip transmission line are connected via a metallized blind via; The first microstrip transmission line includes two end lines and a convex line, the convex line is located between the two end lines and forms a coupling region, the second microstrip transmission line includes a first line and a second line, the second line is perpendicular to the first line; The first circuit overlaps with the circuits at both ends and is connected via metallized blind vias. The second circuit corresponds to the coupling region and is connected to the convex circuit via metallized blind vias.

2. The microstrip filter according to claim 1, wherein The ground plate includes a first dielectric substrate and a second dielectric substrate. The first dielectric substrate is located on an upper layer of the lower microstrip board, and the second dielectric substrate is located on a lower layer of the lower microstrip board.

3. The microstrip filter according to claim 1, wherein The first microstrip transmission line and the second microstrip transmission line are copper foils attached to the upper and lower layers of the upper microstrip board, respectively.

4. The microstrip filter according to claim 1, wherein The length of the microstrip filter is 1 wavelength.

5. A microwave circuit, characterized in that: The microstrip filter comprises the microstrip filter according to any one of claims 1 to 4.

6. An antenna, characterized in that: The microstrip filter comprises the microstrip filter according to any one of claims 1 to 4.

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